The present invention relates to servo actuators of the type employing a low voltage high RPM direct current motor of the relatively low torque sub-fractional horsepower variety. Such devices are commonly employed in motor vehicles for power seat adjustment, movement of engine coolant valves and other valves employed in engine and emission control systems. In such motor vehicle applications, it is known to have the high RPM, low torque motor engage a speed reducer, commonly a gear train, mounted in a common housing with the motor. Where a numerically high ratio of speed reduction or torque multiplication is required, it has been found convenient and desirable to employ a worm on the motor shaft to engage a worm gear for the first stage of speed reduction or torque multiplication.
Where a worm driven speed reducer is employed, the torque reaction of the worm gear on the motor shaft in the axial direction has been found to apply undue thrust loads on the motor bearings and to cause problems with wear of the motor bearings and also to cause a prohibitive amount of noise during operation of the servomotor.
Furthermore, upon assembly of the motor into the servo actuator housing and into engagement with the gear train, it has been required to assemble the motor manually into the housing by first tilting the motor with respect to the housing to engage one end of the motor and then to secure the opposite end of the motor with the drive worm thereon into the housing for engagement with the worm gear. This requirement for tilting of the motor has required manual dexterity and has precluded automation of the assembly of the motor into the housing and has thus resulted in a relatively high cost for the servo actuator assembly in high volume mass production.
In addition, it has been required to accurately locate the motor in the housing to position the worm for proper engagement with the worm gear and to maintain the motor in this position when subjected to the axial thrust of the torque reaction from the driven gear on the motor shaft.
It has thus been found necessary to provide a limit stop in the motor housing for the axial movement of the motor shaft once the motor is installed in the housing. This limit stop acts as a thrust bearing during the operation of the motor under load; and, therefore the limit stop must be accurately located with respect to the front face of the motor upon assembly of the motor in the housing. Referring to FIG. 5, the motor is indicated at 1 with the limit stop denoted by reference numeral 2 and the registration surface for the front face of the motor denoted 3 with the control distance for locating the motor denoted by the character D.
Referring to FIG. 6, a known motor installation technique is indicated where the motor 4 has a spacer 5 provided between the front end face of the motor and the registration surface 3; and, the motor is retained thereon by threaded fasteners such as screws denoted by reference numeral 6. This type of assembly requires several manual operations at assembly and is deemed prohibitively costly for high volume mass production.
Referring to FIG. 7, another technique employed for mounting a servo motor 8 is illustrated wherein an undercut is provided in the stanchion 9 for supporting the rear end of the motor. Assembly of this arrangement requires tilting the motor.
Thus, it has been desired to provide an improved way or means of mounting a low voltage, high RPM relatively low torque direct current servo motor in a servo actuator housing in a manner which does not require manual operations for assembly of the motor and lends itself to automated assembly operations and thereby minimizes the manufacturing costs for high volume production.
The present invention provides a way of mounting a low voltage, high RM. relatively low torque motor of the subfractional Horsepower variety in a servo actuator housing in a manner which permits the motor to be positioned with the motor shaft parallel to its installed orientation adjacent the housing and then moved in solely a single direction normal to the shaft to install the motor in its mounts. The invention particularly relates to motors intended to have a drive worm attached to the motor shaft for engagement with a driven gear as part of a speed reducer within the housing. The present invention employs a resiliently deflectable stanchion for supporting the back or rear end of the motor opposite the motor shaft and a front stanchion spaced from the rear stanchion which permits the motor to be moved in the single direction normal to the motor shaft into the stanchions in a snap locking engagement. The rear stanchion includes a cam surface thereon for deflecting the stanchion as the motor is inserted. The rear stanchion is operable to resiliently bias the installed motor in an axial direction to register the front face or shaft end of the motor against a registration surface on the front stanchion. The housing includes a limit stop or thrust bearing surface located to control axial movement of the motor shaft in operation. In the preferred practice the housing has the front and rear motor stanchions and limit stop molded as a one piece member.